This application describes experiments designed to further test and extend a new theory on structure and reactivity in organic chemistry, developed in the principal investigator's laboratory. The work will cover substituent effects on the aliphatic Claisen rearrangement and on [1,3] and [1,5] sigmatropic migrations. The regiochemical predictive capabilities of the theoretical model will be tested for the first time. Experiments designed to help in the development of a general quantitative theory will be conducted. The predictions of the existing model concerning the existence of new, synthetically useful reactions will be tested. A new hypothesis for the mechanism of the chorismic acid rearrangement will be investigated. The model, in general, is designed to be a tool for synthetic organic chemists, including those engaged in the syntheses of pharmaceuticals. The specific work on chorismic acid could lead to the development of a new class of mechanism-specific antibiotics.